Do CTG expansions at the SCA8 locus cause ataxia?

To evaluate the significance of expanded CTG repeats at the SCA8 locus, we analyzed the allele distribution in 1,262 German ataxia patients. We found intermediate and expanded CTG repeats with similar frequencies in ataxia patients with and without established genetic diseases. One family linked to the SCA8 locus showed incomplete penetrance and an association of smaller CTG repeats with more severe disease. Our data question the disease-causing character of CTG expansions for SCA8 and advise great caution in genetic testing.